What is CSTR (perfectly stirred reactor)?
Gas is fed and withdrawn continuously and reacts while perfectly mixed. The model finds the steady state where inflow, outflow and reaction balance.
Gas that flows in is assumed to mix instantly and completely with the partly reacted gas already inside. It suits continuous combustors and well-mixed reactors, and shows when the residence time is too short for the reaction to keep going (blow-out).
With a mean residence time of 2 seconds, not every bit of gas reacts for 2 seconds: some leaves at once, some stays longer, and 2 seconds is the average. It is like adding cold water slowly to a well-stirred pot: the whole pot cools a little at once.
The CSTR block feeds its inlets (one or more, mixed adiabatically) into a fixed-volume reactor, takes out the same flow so that the operating pressure (default: the inlet pressure) is kept, and finds the steady state with Cantera. Give either the reactor volume or the mean residence time (not both). With the residence time given, the volume follows from the steady-state density. The time integrated to find the steady state is not the residence time; if the balances do not close within its limit, the calculation is an error and no result is shown. Because there may be several steady states, the result records where the solution started (equilibrium = burning branch, inlet = unburned branch).
Compared with the Residence Time Reactor
- Inflow / outflow: none while reacting / continuous
- Meaning of time: the given reaction time / the mean residence time
- Mixing with new gas: no / yes
- Main result: the state after the given time / the steady outlet state
- Main use: kinetics and time behaviour / continuous reactors
At steady state, for every species k
\dot{m}\,(Y_{k,\mathrm{in}} - Y_k) + \dot{\omega}_k W_k V = 0
and for the energy \dot{m}\,(h_{\mathrm{in}} - h) + \dot{Q} = 0. Both balances are checked after the calculation; a result that does not close them is refused. The mean residence time uses the reactor (= outlet) density: \tau = \rho V / \dot{m}. For a first-order reaction A \to B, x_A = 1/(1 + k\tau): less conversion than a batch over the same time, e^{-k t}.
The first version is gas phase, ideal gas, constant volume and steady state.